EP0891299A1

EP0891299A1 - METHOD FOR PREPARING SPINEL Li 1+XMn 2-XO 4+Y INTERCALATION COMPOUNDS

Info

Publication number: EP0891299A1
Application number: EP97917845A
Authority: EP
Inventors: Vesselin Manev; Walter Ebner; William Thompson; Stephen Dow
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1996-04-05
Filing date: 1997-04-02
Publication date: 1999-01-20
Anticipated expiration: 2017-04-02
Also published as: US6280699B1; US5789115A; JPH11509827A; DE69702839D1; DE69702839T2; AU2606897A; EP0891299B1; WO1997037935A1; ATE195495T1; US5961949A

Abstract

A method of preparing a highly homogenous spinel Li1+XMn2-XO4+Y intercalation compound having a predetermined mean particle size and particle size distribution for 4 V secondary lithium and lithium ion cells is provided. The method comprises mixing at least one manganese compound having a predetermined particle size distribution with at least one lithium compound wherein the manganese compound has a mean particle size of between about 1 and 15 microns and the mean particle size of the lithium compound is less than that of the manganese compound The mixture is then fired in one or more firing steps within specific temperature ranges to form the Li1+XMn2-XO4+Y intercalation compound. Preferably, at least one firing step is at a temperature of between about 700° C. and 900° C. The Li1+XMn2-XO4+Y intercalation compounds may be used in the positive electrodes of secondary lithium and lithium ion cells to provide cells having high specific capacity, cycleability, and charge-discharge rate capability.

Description

METHOD FOR PREPARING SPINEL Li_1+xMn₂__x0_4+v INTERCALATION COMPOUNDS

FIELD OF THE INVENTION This invention relates to spinel Li_1+xMn₂__x0_4+Y intercalation compounds, and particularly to the use of spinel Li_1+xMn_2-x0_4+Y intercalation compounds in 4 V secondary lithium and lithium ion batteries.

BACKGROUND OF THE INVENTION Heretofore, lithium intercalation compounds such as Li_ltXMn₂__x0_4+Y have been used in positive electrodes for 4 V secondary lithium and lithium ion batteries. The spinel LiMn₂0₄ intercalation compound was first obtained by ickham and Croft by heating lithium carbonate and manganese oxide in a 1:2 lithium to manganese molar ratio. D. G. Wickham and W. J. Croft, Crystal lographic and Magnetic Properties of Several Spinels Containing Trival ent JA - 1044 Manganese; J . Phys. Chem. Solids 7, 351-360 (1958) . As demonstrated in U.S. Pat. No. 4,426,253 to Hunter, the acid treatment of LiMn₂0₄ forms a λ-Mn0₂ which can be used in a positive electrode for electrochemical'power sources. It was later discovered that the spinel

LiMn₂0₄ could be used as the positive electrode for a secondary lithium cell. Thackery et al . , Li thium Insertion Into Manganese Spinels ; Material Research Bulletin 18, 461-472 (1983) . - 2 -

The mean particle size and the particle size distribution are two of the basic properties characterizing the positive electrode intercalation materials for secondary lithium batteries. These properties are considered to be important because they directly influence the charge-discharge rate capability, the safety cell performance, the electrode formulation and the electrode coating process of positive electrodes containing these materials. In addition, a decrease in the mean particle size and distribution of the intercalation compounds typically results in an increase in the cycleability of these compounds. The reason for the increase in cycleability is that smaller particles are relatively more flexible than larger particles and therefore the changes in the crystal lattice parameters which occur during cycling do not damage the cycleability of the smaller particles to the degree that the larger particles are damaged.

Nevertheless, a decrease in the mean particle size results in a significant increase in the electronic resistivity of the spinel compounds . The electronic resistivity is controlled by the contact resistivity between the particles which rises significantly due to an increase in the number of contact boundaries which the electrons have to overcome. The increase in electronic resistivity leads to an increase in the electrode polarization which decreases both the specific capacity and charge- discharge rate capability of the electrode. Furthermore, a decrease in the particle size is generally coupled with an unwanted decrease in the tapped or powder density. Because many batteries such as batteries for electronics have fixed volumes, it is preferred that the spinel material used in the positive electrode of these batteries has a high tapped density, so there is essentially more chargeable material in the positive electrode. A higher tapped density results in a positive electrode having a higher overall capacity. Therefore, depending on the nature of the intercalation compounds and the electrode formulation, the cycleability, specific capacity, tapped density and charge-discharge rate of the spinel material should be considered in determining a desirable particle distribution for the spinel material.

Accordingly, these factors have been considered in the preparation of LiCo0₂ intercalation compounds, where the desired particle size has been achieved by grinding the LiCo0₂ material. Nevertheless, grinding Li_1+xMn₂__x0_4+Y intercalation compounds results in a considerable reduction in specific capacity. V. Manev et al . , Rechargeable Li thium Ba t tery Wi th Spinel - delated λ -Mn0₂. Part III . Seal ing - up Problems

Associa ted Wi th LiMn₂0₄ Synthesis , J. Power Sources 54, 323-328 (1995) . As described in this article, the reduction in specific capacity is due to changes in the Li_1+xMn₂__x0₄„_Y structure which occur as a result of the stress of mechanical treatment, measured by the contraction of the crystal lattice parameter a. Therefore, grinding the Li_1+xMn₂__x0_4tY material is not a desirable method of reducing the mean particle size and particle size distribution of spinel Li_1+xMn₂__x0_4+Y intercalation compounds.

SUMMARY OF THE INVENTION The present invention provides a method of preparing a spinel Li_1<xMn₂__x0_4+Y intercalation compound having a predetermined mean particle size and particle distribution for 4 V secondary lithium and lithium ion cells having high cycleability, specific capacity, and charge-discharge rate capability.

The method of preparing the spinel Li_1+xMn₂__x0_4+Y intercalation compound comprises mixing at least one manganese compound with at least one lithium compound and firing the mixture in one or more steps within specific temperature ranges. The temperature ranges of the firing steps fall between about 450°C and 900°C with at least one firing step at a temperature of between about 700°C and 900°C to form the Li_ltXMn_?__x0_4tY intercalation compound. Typically, the mean particle size of the lithium compound used to form the spinel is less than the mean particle size of the manganese compound thereby allowing the lithium particles to be uniformly dispersed with the manganese particles. Preferably, the manganese compound used to form the spinels has a predetermined mean particle diameter of between about 1 and 15 microns and a predetermined particle size distribution wherein at least about 99% of the particles have a diameter of less than about 40 microns. In addition, the manganese compounds preferably have a narrow particle size distribution wherein the maximum particle diameter is less than about 10 times the mean particle diameter and/or at least about 90% of the particles are distributed in a range not wider than about one order of magnitude.

The spinel Li_1+xMn₂__x0_4tY intercalation compounds prepared according to the present invention have a predetermined mean particle size and particle size distribution generally corresponding to the size of the particles in the manganese compounds. Therefore, the predetermined mean particle size and particle size distribution is achieved without any additional mechanical treatment, e.g., grinding, of the spinel Li_ltXMn_?__x0_4tY compounds. The Li_1+xMn₂__x0_4+Y intercalation compounds may be used in the positive electrodes of secondary lithium and lithium ion cells to provide cells having high cycleability, specific capacity and charge-discharge rate capability.

These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings which describe both the preferred and alternative embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph illustrating the comparison between the particle size distributions of the starting Mn0₂ and the spinel Li_1+xMn₂__x0_4tY mixture obtained from firing a mixture of the Mn0₂ and LiOH at 750°C for 48 hours .

FIG. 2 is a graph illustrating the comparison between the particle size distributions of the starting Mn0₂ and the spinel Li_ltXMn₂__x0_4+v compound obtained from firing a mixture of the Mn0₂ and Li₂C0₃ at 850°C for 48 hours .

FIG. 3 is a graph illustrating the comparison between the particle size distributions of the starting MnC0₃ and the spinel Li_1+xMn₂__x0_4tY compound obtained from firing a mixture of the MnC0₃ and LiN0₃ at 750°C for 48 hours.

FIG. 4 is a graph illustrating the comparison between the particle size distribution of a spinel prepared according to the invention and a spinel prepared from a lithium compound having a larger mean particle size according to a comparative example.

FIG. 5 is a graph illustrating the comparison between the particle size distribution of a spinel prepared according to the present invention and the same spinel compound ground for about 10 minutes in a ball mill according to a comparative example.

DETAILED DESCRIPTION OF THE INVENTION It has been discovered that according to the method of the present invention, spinel Li_l4XMn_{2 x}0_4+Y material having a predetermined mean particle size and a narrow particle distribution may be prepared without further mechanical treatment and losses in specific capacity, cycleability, tapped density and charge- discharge rate capability. The spinel Li,_lXMn_{? x}0_4÷v material is prepared from a starting mixture which includes at least one manganese compound and at least one lithium compound. The at least one manganese compound is selected from the group consisting of manganese salts and manganese oxides. Exemplary manganese salts and oxides include Mn0₂, Mn_?0₃, Mn_?0₄, MnC0₃, MnS0₄, Mn(N0₃)₂, MnOOH, Mn(CH₃C0₂)₂, and mixtures thereof. The at least one lithium compound is selected from the group consisting of lithium salts and lithium oxides. Exemplary lithium salts and oxides include Li₂0, LiOH, LiN0₃, Li₂C0₃, Li,S0₄ , LiN0₃, LiCH₃C0₂, and mixtures thereof . The at least one manganese compound and at least one lithium compound are mixed in a lithium to manganese mole ratio of between about 1.02:2 and 1.1:2.

In order to provide highly homogenous spinel Li_ltXMn_2^x0_4+Y intercalation compounds having a predetermined mean particle size and narrow particle size distribution, the particle size of the starting materials, specifically the manganese compound is controlled. The manganese compound has a predetermined mean particle diameter of between about 1 and 15 microns, preferably between greater than 1 to about 15 microns and more preferably between about 5 and 15 microns, and a predetermined particle size distribution wherein at least about 99% of the particles have a diameter of less than about 40 microns. Additionally, the maximum particle diameter of the manganese compound is typically less than about 10 times the mean particle diameter and preferably less than about 5 times the mean particle diameter. The manganese compound is preferably highly homogenous wherein at least about 90% of the manganese compound particles are distributed in a range not wider that about one order of magnitude.

The manganese compound may be ground such as by a ball or jet mill to provide the desired particle size used in the invention.

The lithium compound used to form the spinel Li_ltXMn₂._x0_4+Y intercalation compounds of the present invention typically has a smaller mean particle size than the manganese compound used. Preferably, the mean particle size of the lithium compound is at least two to three times lower than that of the manganese compound. The smaller particle size lithium compounds become more uniformly dispersed with the manganese compound particles upon mixing to provide more homogenous spinel compounds with increased cycling lives. Preferably, the mean particle size of the lithium compound is between about 0.5 and 5 microns, more preferably between about 1 and 3 microns. The lithium compound may be ground such as by a ball or jet mill to provide the desired particle size used in the invention. However, the lithium compound and manganese compound are preferably ground separately to provide a lithium compound having a smaller mean particle size than that of the manganese compound used in the invention.

In order to form the spinel Li_ltXMn_{2 x}0_4<γ intercalation compounds, the at least one manganese compound having a predetermined particle size and particle distribution and the at least one lithium compound having a predetermined mean particle size less than that of the manganese compound are mixed together and fired in one or more steps within specific temperature ranges which fall between 450°C and 900°C. Preferably, at least one firing step is at a temperature of between about 700°C and 900°C. In this firing step, the temperature is maintained between about 700°C and 900°C for a soak time of at least about 10 hours, and preferably for at least about 24 hours, to form the spinel Li_1+xMn_{2 x}0_4+γ material . In order to provide a spinel having enhanced properties, the mixture may be subjected to an additional firing step at a temperature range of between about 400°C and 600°C for at least about 12 hours prior to the 700°C-900°C firing step. Additionally, the mixture is generally fired in the presence of a gas flow such as air or a gas mixture containing from 5 to 100 percent oxygen by volume . Suitable firing step sequences are described in commonly owned applications entitled "Highly Homogenous Spinel Li_1(XMn_{2 x}0₄ Intercalation Compounds and Method for Preparing Same", Serial Nos. 08/665,396 and 08/665,408, filed concurrently on June 18, 1996 and incorporated herein in their entirety by reference. Any of the firing steps used to form the spinel may include changes in the temperature within the described ranges. In other words, the temperature may be increased or decreased within the described ranges during the firing step. Although the firing temperatures are preferably maintained for the soak times described above, longer soak times tend to provide an improved spinel compound. Nevertheless, the soak times are typically dictated by commercial feasibility and extremely long soak times may not be desired.

In accordance with one aspect of the present invention a spinel Li_1<xMn₂__x0_4+Y with strictly defined particle size and particle size distribution is provided by firing a reaction mixture of the manganese compound and the lithium compound in one or more firing steps with at least one firing step at a temperature of between about 700°C and 800°C, preferably between about 730°C and 770°C, and more preferably up to about 750°C. In this temperature range, the particle size distribution of the final Li_1+xMn_{2 x}0₄,_γ essentially corresponds to the particle size distribution of the starting manganese compound.

In accordance with another aspect of the present invention, a spinel Li_1<xMn₂__x0_4+Y with controlled particle size and particle size distribution is provided by firing a reaction mixture of the manganese compound and the lithium compound in one or more firing steps with at least one firing step at a temperature of between about 800°C and 900°C, preferably between about 800°C up to about 850°C, and more preferably about 825°C. In this temperature range, the particle size distribution of the Li_ltXMn₂__x0_4+Y spinel material is directly related to the particle size distribution of the starting manganese compound. Nevertheless, in this temperature range, there is generally an offset between the particle size distribution of the Li₁,_xMn₂._x0_4+Y material and the particle size distribution of the starting manganese compound corresponding to an increase in the particle size of the spinel material at the higher temperature range. For example, the mean particle size of the spinel is between about 10 and 15 microns when the mean particle size of the manganese compound is between about 6 and 7 microns when the starting materials are fired at between about 800°C and 900°C. In both the low temperature range (700°C-800°C) and the high temperature range (800°C-900°C) , the Li_ltXMn₂__x0_4+Y intercalation compounds are highly homogenous and possess a high specific capacity, cycleability, tapped density and charge-discharge rate capability.

The spinel Li_1+xMn₂__x0₄,_y intercalation compounds prepared according to the present invention possess improved properties over conventional Li₁,_xMn_{2 x}0_4+γ spinels. The spinel Li_ltXMn_{2 x}0_4<γ of the invention is a highly ordered and homogeneous structure having a low capacity fade during cycling. The improved physicochemical and electrochemical properties of the Li_1+xMn₂__x0_4+Y spinels of the invention are independent of the specific manganese and lithium compounds used to form the spinel but are dependent instead on the particle size of the manganese and lithium compounds. The spinel Li_1(XMn₂._x0_4)Y compounds may be used in positive electrodes in electrochemical cells. The Li_1+xMn₂__x0_4tY spinel material is typically combined with a conductive agent such as graphite or carbon black and a binder material such as polyvinylidene difluoride (PVDF) and dispersed in a solvent such as n-methyl pyrrolidinone (NMP) (e.g. 1-methyl-2-pyrrolidinone) to form a slurry. The slurry is typically spread on an aluminum current collector and then heated to evaporate the solvent to form a dry electrode material. The dry electrode is then compressed by rolling, pressing, or other known methods, and cut into, for example, a disk, to form the positive electrode. The electrode is then placed inside an electrochemical cell with a lithium counterelectrode and an electrolyte such as EC:DMC/LiPF₆.

The present invention will be further illustrated by the following nonlimiting examples.

EXAMPLE 1 Chemical grade MnO_? particles were subjected to preliminary grinding until a mean particle size of 2 microns was obtained. The Li_{x 025}Mn_{1 g75}0₄ sample was produced by heating a 500 g mixture of the ground Mn0₂ and LiOH at a molar ratio 2Li:Mn = 1.05. The mixture was then fired for 48 h at 750°C in a muffle furnace.

The spinel material was cooled by removing the material from the furnace.

The effect of the particle size distribution of the starting Mn0₂ having a mean particle size of 2 microns on the particle size distribution of the

Li-i_.o2sMⁿi ₉₇₅0₄ is illustrated in FIG. 1. FIG. 1 shows that the particle size distributions of the Mn0₂ starting material and the final Lij ₀25^Mn _{ι s}iA correspond remarkably well . EXAMPLE 2

The Mn0₂ used in Example 1 was mixed with LiC0₃ at a molar ratio 2Li:Mn = 1.1 and fired for 48 h at 850°C in a muffle furnace. The spinel material was cooled by removing the spinel material from the urnace .

The effect of the particle size distribution of the starting Mn0₂ having a mean particle size of 2 microns on the particle size distribution of the final Li_1.05Mn_1.95O₄ is illustrated in FIG. 2. As shown in FIG. 2, firing the Mn0₂ and LiC0 at 850°C shifts the particle size distribution curve of the Li_{x 0},_;Mn_{1 95}0₄ spinel particles to higher values than those obtained using the 750° firing. Despite the higher particle size resulting from 850°C firing, the distribution transforms into an even more symmetrical distribution curve with the maximum particle size of the final product slightly exceeding the maximum particle size of the starting manganese compound. Therefore, as with the material fired at 750°C in Example 1, the particle size and particle size distribution can be defined by particle size distribution curve of the starting compound and by calculation of the offset of the distribution curves after the firing on the basis of the preliminarily obtained experimental data.

EXAMPLE 3

MnC0₃ was subjected to preliminary grinding until a compound with mean particle size of 9 microns was obtained. The Lij ₀₂₅ ^Mn _{ι 97}Α sample was produced by heating a 500 g mixture of the ground MnC0₃ and LiN0₃ at a molar ratio of 2Li:Mn = 1.05. The mixture was fired for 48 h at 750°C in a muffle furnace. The synthesized spinel was cooled by removing the spinel material from the furnace . Even though a small difference is observed in

FIG. 3 in the particle size distribution of the starting MnC0₃ and the final spinel Li_x ^M^ ₉₇ O,._, the difference between the mean particle size of these materials is negligible. The comparison between the mean particle diameters of the starting MnC0₃, (8.49 microns) and the mean diameter of the final spinel

Li_1.o25 ^Mn _ι.97₅°4' (8.88 microns) shows only a 4.5% change from the initial value of the manganese compound.

EXAMPLE 4

The Li_{x 02b}Mn_{1 97b}0₄ sample was produced by heating a 500 g mixture of the MnC0₃ in Example 3 and Li₂C0₃ with a mean particle size of 2.5 microns at a molar ratio of 2Li/Mn = 1.05. After a preliminary treatment at 550°C and 750°C, the mixture was fired at 850°C for 48 hours in a muffle furnace. The synthesized spinel was cooled at a cooling rate of 50°C/hour.

The prepared spinel Li_{x 025}Mn_{1 975}0₄ compound was mixed with 10% graphite and 5% PVDF binder dissolved in NMP solvent to form a slurry. The slurry was spread on aluminum foil and heated to evaporate the NMP solvent. The dry electrode was then pressed at 500 kg/cm² and cut into a disk test sample electrode having a diameter of about 1 cm and a thickness of about 0.015 cm. The prepared test electrode was placed inside an electrochemical cell with a lithium counter electrode and with EC:DMC/LiPF₆ electrolyte and a charging- discharging test was conducted at 1 h charge-discharge rate and 3 - 4.5 V voltage limits.

COMPARATIVE EXAMPLE 1 The Li_1+xMn_2^x0_4tY sample was produced by heating a 500 g mixture of the MnC0₃ in Example 3 and Li₂C0₃ with a mean particle size of 36 microns at a molar ratio of 2Li/Mn = 1.05. The synthesis conditions were exactly the same as in Example 4, where after a preliminary treatment at 550°C and 750°C, the mixture was fired for 48 hours at 850°C in a muffle f rnace. The synthesized spinel was cooled at a cooling rate of 50°C/hour. A spinel Li_{x 025}Mn_{1 97s}0₄ positive test electrode was prepared in the same manner as in Example 4 , an electrochemical cell was assembled in the same manner as in Example 4, and the cell charge-discharge characteristics were measured under the same conditions as Example 4.

COMPARATIVE EXAMPLE 2 The Li_{x ϋ25}Mn_{1 975}0₄ sample was prepared by grinding the spinel L^ ^Mn-_{L 975}0₄ compound described in Example 4 in a ball mill for about 10 minutes. A spinel Li_{2 02s} ^Mn _ι.97₅O positive test electrode was prepared in the same manner as in Example 4 , an electrochemical cell was assembled in the same manner as in Example 4, and the cell charge-discharge characteristics were measured under the same conditions as Example 4.

The comparison between the particle size distribution of the spinel compound prepared according to Example 4 and Comparative Example 1 is illustrated in Fig. 4. Fig. 4 demonstrates that the particle size of the lithium compound, which differs in the two examples by more than one order of magnitude, does not have any effect on the particle size distribution of the final spinel compound. However, as shown in Table 1 below, the comparison between the cycleability of the spinel compounds prepared according to the Example 4 and Comparative Example 1 demonstrates that the cycleability of the spinel prepared by using a lithium compound with a smaller particle size than the manganese compound is considerably better than the cycleability of the spinel prepared by using a lithium compound with a larger particle size than the manganese compound. Specifically, after fifty cycles, the specific capacity of the spinel in Example 4 decreases only 2.4% compared to 8.1% for Comparative Example 1. - 14 - TABLE 1

Specific capacity (mAh/g)

First Cycle Twentieth Fiftieth Cycle Cycle

EXAMPLE 4 123 121 120

COMPARATIVE EXAMPLE 1 124 117 114

The comparison between the particle size distribution of the spinel prepared according to Example 4 and the particle size distribution curve of the ground spinel according to Comparative Example 2 is illustrated in Fig. 5. Fig. 5 shows a negligible decrease in the particle size distribution after the grinding procedure. In contrast, Table 2 demonstrates the comparison between the specific capacity of the spinels after numerous cycles. As shown in Table 2, both the initial specific capacity and the cycleability of the spinel is considerably decreased after grinding the spinel particles. In particular, the specific capacity of Example 4 after fifty cycles decreases only 2.4% compared to 11.8% for Comparative Example 2. This shows that grinding of the final spinel Li_1÷xMn_{2 x}0_4+γ results in a strong negative effect on its electrochemical performance .

TABLE 2

Specific capacity (mAh/g)

First Cycle Twentieth Fiftieth Cycle Cycle

EXAMPLE 4 123 121 120

COMPARATIVE EXAMPLE 2 119 110 105 It is understood that upon reading the above description of the present invention, one skilled in the art could make changes and variations therefrom. These changes and variations are included in the spirit and scope of the following appended claims.

Claims

CLAIMS : 1. A method of preparing a spinel Li_1+xMn_:, _x0₄,_γ intercalation compound comprising: mixing at least one manganese compound selected from the group consisting of manganese salts and oxides with at least one lithium compound selected from the group consisting of lithium salts and oxides, wherein the manganese compound consists of particles having a mean particle diameter of between about 1 and 15 microns; and firing the mixture from the mixing step in one or more steps within specific temperature ranges to form the spinel Li_lfXMn_{2 x}0_4+γ intercalation compound wherein at least one step is at a temperature of between about 700°C and 900°C.

2. A method of preparing a positive electrode for an electrochemical cell comprising:

(a) mixing at least one manganese compound selected from the group consisting of manganese salts and oxides with at least one lithium compound selected from the group consisting of lithium salts and oxides, wherein the manganese compound consists of particles having a mean particle diameter of between about 1 and 15 microns; (b) firing the mixture from the mixing step in one or more steps within specific temperature ranges to form the spinel Li_1^xMn₂__x0_4tY intercalation compound wherein at least one step is at a temperature of between about 700°C and 900°C; (c) dispersing the Li_ltXMn₂__x0_4+Y spinels in a solvent with a conductive agent and a binder material to form a slurry;

(d) heating the slurry to evaporate the solvent to form a dry electrode; (e) compressing the dry electrode; and (f) cutting the dry electrode to form a positive electrode for an electrochemical cell .

3. The method according to claims 1 or 2 wherein the firing step comprises firing the mixture for a period of at least about 10 hours.

4. The method according to claims 1 or 2 wherein the firing step comprises firing the mixture for a period of at least about 24 hours.

5. The method according to claims 1 or 2 wherein the firing step comprises firing the mixture at a temperature of between about 700°C and 800°C.

6. The method according to claims 1 or 2 wherein the firing step comprises firing the mixture at a temperature of between about 800°C and 900°C.

7. The method according to claims 1 or 2 wherein the manganese compound particles of the mixing step have a maximum particle diameter of not greater than about 10 times the mean particle diameter.

8. The method according to claims 1 or 2 wherein at least about 99% of the manganese compound particles has a particle diameter of not greater than about 40 microns.

9. The method according to claims 1 or 2 wherein at least about 90% of the manganese compound particles are distributed in a range not wider than about one order of magnitude .

10. The method according to claims 1 or 2 wherein the firing step comprises firing the mixture at a temperature of between about 730°C and 770°C.

11. The method according to claims 1 or 2 wherein the firing step comprises firing the mixture at a temperature of between about 800°C and 850°C.

12. The method according to claims 1 or 2 wherein the manganese compound is selected from the group consisting of Mn0₂, Mn₂0₃, Mn₃0₄, MnC0₃, MnS0₄, Mn(N0₃)₂, MnOOH, Mn(CH₃C0₂)₂, or mixtures thereof.

13. The method according to claims 1 or 2 wherein the lithium compound is selected from the group consisting of Li₂0, LiOH, LiN0₃, Li₂C0₃, Li₂SO„, LiN0₃, LiCH₃C0₂, or mixtures thereof.

14. The method according to claims 1 or 2 wherein the mean particle size of the lithium compound is less than the mean particle size of the manganese compound.

15. The method according to claim 14 wherein the mean particle size of the lithium compound is between about 0.5 and 5 microns.

16. The method according to claims 1 or 2 further comprising grinding the manganese compound prior to said mixing step.

17. A product prepared according the methods of claims 1 or 2.

18. A spinel Li_1+xMn_{2 x}0_4^γ intercalation compound having a mean particle size of between about 5 and 20 microns.

19. A positive electrode for an electrochemical cell comprising: a Li₁_,_xMn_{2 x}0_4+γ spinel having a mean particle size of between about 5 and 20 microns; a conductive agent; and a binder.

20. The product according to claims 18 or 19 wherein the mean particle size of the spinel is between about 10 and 15 microns.